The availability of sources of coherent electromagnetic radiation at wavelengths in the range of 0.5-5 micrometers and of waveguides for transmitting such radiation have produced widespread interest in the use of light as communications medium. Proposed optical communications systems may comprise light sources, optical waveguides, couplers between light sources and waveguides, and active components such as modulators, deflectors, and switches. Waveguides typically are of a type known as optical fibers or else are patterned transparent films on a substrate. Active components may be integrated with optical fibers as shown in U.S. Pat. No. 3,770,339 (issued Nov. 6, 1973 to V. Ramaswamy) which discloses a device for modulating the intensity of light traveling in an optical fiber by varying an electrical voltage applied to electrodes which are placed circumferentially around the fiber. Another electro-optic device suitable for use with fibers is shown in U.S. Pat. No. 3,918,794 (issued Nov. 11, 1975 to A. F. Milton) which discloses the use of liquid crystal materials for diverting light traveling in optical fibers. Additional devices intended for use with optical fibers are the mechanical and hydraulic deflectors disclosed in U.S. Pat. No. 3,874,779 (issued Apr. 1, 1975 to F. L. Thiel).
Active components have also been disclosed integral to thin film devices; e.g., U.S. Pat. Nos. 3,883,220 (issued May 13, 1975 to H. F. Taylor) and 4,070,092 (issued Jan. 24, 1978 to W. K. Burns) disclose electro-optic devices in which light travels in crystalline thin films. In response to a voltage applied to electrodes disposed on such films, a local change in refractive index is produced in the film, thereby affecting the direction of light propagating in the film.
Electrically controlled coupling of light between parallel waveguides in thin films is disclosed in U.S. Pat. Nos. 3,589,794 (issued June 24, 1971 to E. A. J. Marcatili), 3,781,081 (issued Dec. 25, 1973 to G. H. S. Rokos), 4,026,632 (issued May 31, 1977 to K. O. Hill), 3,909,108 (issued Sept. 30, 1978 H. F. Taylor), and 3,964,819 (issued June 22, 1976 to F. Auracher).
In addition to electro-optic devices as referred to above, devices have been proposed for deflecting light traveling in thin films by acoustical and magnetic means. Instances of such devices are disclosed, respectively, in U.S. Pat. Nos. 4.027,946 (issued June 7, 1977 to C. S. Tsai) and 3,870,398 (issued Mar. 11, 1975 to J. F. Dillon). Moreover, coupling of light between thin film waveguides may be effected acoustically, magnetically, or by piezoelectrically induced mechanical motion of grating couplers as disclosed in U.S. Pat. No. 4,013,000 (issued Mar. 22, 1977 to H. W. Kogelnik).
In spite of longstanding recognition of the feasability of optical communications as discussed, e.g., by Stewart E. Miller, "Integrated Optics: An Introduction", Bell System Technical Journal, Volume 48, Number 7 (September 1969) and notwithstanding the variety of components disclosed in patents cited above, the search continues for reliable, commercially viable optical components which are readily combined into integrated systems. In particular, there is a need for active components such as switches and modulators which can be integrated into systems based on light propagating in amorphous and polycrystalline waveguides. One answer to this need is disclosed below, another is disclosed in copending U.S. patent application Johnson-Singh-Van Uitert Ser. No. 973,162.